Motor-generator gearing



Dec. 2U, w55 A. 1. ALSTROM ZTW MOTOR-GENERATOR GERNG Filed Nov. 19, 1954 5 Sheets-Sheet l IN V EN TOR. fil/5er? l ./isff'om, BY

Dec. 20, 1955 A. 1. ALSTROM 2,727,410

MOTOR-GENERATOR GEARING Filed NOV. 19, 1954 5 Sheets-Sheet 2 mi IINE i: iwf Z Il j Q y i352; I @u l n l "77 @D 1 6 f5 l I I l i i @zy I0.

JNVENTOR. z/erzz fihi/01m BY Dec. 20, 1955 A. l, ALsTRoM 2,727,410

MOTOR-GENERATOR GEARING Filed NOV. 19, 1954 5 Sheets-Sheet 5 W l j j? 7 5254 i l a /Y jj ,7- ff INVENTOR. fler Z /szfam,

Q, @@QPM Dec. 20, 1955 A. l. ALSTROM 2,727,410

MOTOR-GENERATOR GEARING Filed NOV. 19, 1954 5 Sheets-Sheet 4 Dec. 20, 1955 A. 1. ALsTRoM 2,727,410

momia-GENERATOR GEARING Filed Nov. le), 954 5 Sheets-Sheet 5 INVENTOR. .f7/erf .f7/. from,

United States. dPatent 2,727,410 MOTOR-GENERATOR 4(maillist:

Albert I. Alstrom, Longmeadow, M ass.',.assignor to Wico Electric Company, West Springlelld,rMass., a corporation of Massachusetts f i Application November 19, 1954, SeralNo: 470,094"= 6 Claims. (Cl. 749-810)l This invention relates to improvements in transmissions for interconnecting a dynamo-electric machine and an internal combustion engine, so that the one-4 machine may serve as a motor to crank the engine and'subsequ'entl'y as a generator, driven by the engine, `to* `supply electricity for charging a storage battery which, is subsequently used =to supply electricity to the dynamo-electric ymachine;*vi/hen serving as a motor. f l 2 An object of the invention is to provide inan'electric motor-generator, having an armature shaft; 'a tirsttransmission from said shaft, Vadapted for connection lto fan internal combustion engine and including a'" one-way clutch, whereby such shaft may be driven from the engine but cannot drive the same; an enginelstarter drive, includ'- ing a screw-shaft and a pinion engaged therewith for movement longitudinally thereof into' and out of mesh with the ywheel gear of the engine; and-.a second transmission interconnecting the armature shaft and the screwshaft of the engine-starter drive and including a centrifugal clutch for interrupting the drive to the enginesstarter drive, when the engine starts.

Another object of the invention is to provide inan arrangement of the class described, a centrifugal clutch which includes a pawl mounted on a carrier, which is indriving engagement with the armature shaft, and engageable in a notch in a disk, which is in driving engagement with the engine-starter drive, said pawl being movable out of said notch by centrifugal force, when the speed of the engine shaft exceeds a predetermined-very lowyalue and the engine-starter drive is unloaded.

Another object of the ,invention is `tta-:provide in' an arrangement of the class described; a shoulder, forming one wall of the notch of the aforesaid disk and yadapted to be engaged by the driving face of the pawl, such face and such wall being so related Athat the Ypawl cannot be swung out of the notch by centrifugal force while the disk is under load, but only after the disk yhas been moved forwardly ahead of the driving face of the'p'awlwhich occurs when the disk is unloaded by cam' action of the'face on said wall when the pawl is swung-outwardly under the action of centrifugal force.

Another object of the invention is to provide in an arrangement of the class described, spring means for moving the pawl in opposition tothe'action of centrifugal force, such means exerting pressureV on the pawl which pressure is automatically variable from aminimumfwhen the pawl is disengaged from a notch in the disk, toa maximum, when the pawl is engaged-'in such notch, whereby a very low spring pressure may be utilized to prevent the pawl from moving into the notch until the engine has reached 4stalling speed rand -is practically stopped, and a much greater spring pressure may be utilized to hold the pawl engaged in the notch in a stable manner without uttering. f

A further object of the invention `is toY provide an adjustable mounting for the motor-generator on an `engine for tensioning an endless member, which drivesthe gen? erator from the engine, such mounting enabling the motor- 2,727,410 Patented Dec. 20, 1955 ce A l geueratorto swing about the axis of the engine-starter drive. i

:The: invention will be disclosed with reference to the one illustrative embodiment of it shown in the accompanyiug drawings, in which,

Tf Fig l; is a top `plan view showing a starter-generator and transmissions, embodying the invention, for interconnecting it to an internal combustion engine;

Fig. 2 is a exterior elevational View thereof;

*Figi-3 is a sectional elevational view taken on the line 3;-3-ofFig.V l;`

'rFig. 4 is a sectional plan View, taken on the line 4--4 of Fig. 3 and drawn to a larger scale;

Fig. 5 is a sectional plan view taken on the line 5-5 of Fig.` 3 and drawn to a larger scale;

Fig. 6 is -a fragmentary elevational View illustrative of the mounting vof f the driving pawls of the centrifugal clutch;

'-Fig. 7 is a fragmentary elevational View taken at right angles to Fig. 6 and showing a detail of the mounting of the driving pawls of the centrifugal clutch;

Fig. 8 is a fragmentary sectional-plan View, taken simiiarly toFig. 4 but showing one of the pawls of the centrifugal clutch in released position;

9 Fig. 9-is a sectional plan View taken on the line 9-9 of Fig. 3;

Fig. 10 is a sectional plan view taken on the line 10-10 of Fig. 3; and

Fig. l1 is a diagram of the electrical circuits for the motor-generator.

Referring to these drawings; there is shown in Figs. l and 2 a portion of the casing 1 of an internal combustion engine, its crankshaft 2, flywheel 3, and gear 4 fixed to the latter; The particular engine, herein shown, is an outboard motor and its crankshaft 2 is vertically disposed with the ywheel 3 uppermost and adapted to rotate clockwise as viewed in Fig. l. K

This invention provides a dynamo-electric machine which may function as a motor to drive the engine for starting purposes, and as a generator, driven by the engine, for supplying electricity for charging the storage battery that supplies current for the starting motor. This electric motor-generator is contained within a housing consisting of a hollow cylindrical shell 5, a lower end bell 6 and an upper end member 7, all suitably held together, as by a plurality of screws 8. The shell 5 (Fig. 9) carries a series of radial cores 9 on which are mounted the eld windings 10 and'11 for the motor and generator, respectively.` There is a single armature 12, having suitable windings 13 suitably connected to a commutator 14. This armature (Fig. 3) is fixed to a shaft 15, mounted in suitable bearings, such as a lower ball thrust bearing 16 in end bello, and an upper ball bearing 18, mounted in a casing 19 which is xed to end member 7 by screws 20. This casing 19 and end member 7 cooperate to form a housing for enclosing the transmission by which shaft 15 drives the engine-starter drive and cranks the engine. This shaft extends freely through a hollow hub 17 on member 7 and upwardly above member 19 for connection to means by which it may be driven from the engine as will later appear.

The housing of the motor-generator is supported from the engine casing 1 by means of a bracket 21 (Fig. 2), suitably xed thereto, as by screws 22, and having upper and lower outstanding ears 23 and 24, respectively. The upper end member 7 has depending therefrom a boss 25, the lower end face of which rests on the upper face of ear 23 and is clamped thereto by a screw 26. This screw has a smooth cylindrical portion 27 which is rotatably engaged in ear 23. Underlying the lower ear 24 g isa boss 28, projecting from the end bell 6 and carrying a screw 29, which has a smooth cylindrical portion 30 3 rotatably engaged in ear 24 and axially aligned with screw 27. When the latter is loosened, the housing of the motor-generator may be swung about the vertical axis of the aligned pivots 27 and 30 for a purpose to be later described. When screw 26 is tightened the housing is clamped rrniy to ear 23 and thus to the engine housing.

There are two transmissions between the armature shaft and the crankshaft 2. One transmission (Figs. l and 2) includes a grooved pulley 31, fixed to the upper end of the crankshaft 2; a grooved pulley 32, mounted on the upper end of the armature shaft 15; a V-belt 33 interconnecting the pulleys 31 and 32; and a suitable overrunning or one-way clutch, which is mounted within the pulley 32, as will be later described, and which enables this shaft to turn during cranking of the engine, when the pulleys 31 and 32 and belt 33 are initially at rest. This first transmission is for the engine to drive the armature for generating electricity to charge a storage battery. The other transmission includes an engine-starter drive (Fig. 3) which includes a pinion 34, mounted on a vertical shaft and adapted to be automatically moved longi udinally into engagement with the iiywheel gear 4 for the purpose of starting theengine and out of engagement with the flywheel after the engine has been started. It will be noted that shaft 35 is located coaxially of the pivots 27 and 30, which, as above described, connect the housing of the motor-generator to the engine casing 1. Consequently, the housing can be moved on these pivots to adjust the tension of belt 33 without displacement of the other driving connection with the engine ywheel.

In the particular engine-starter drive, herein shown, the shaft 35 has on an intermediate portion a plurality of splines 36, with which is slidably engaged a member 37 having a triple screw thread 38 engaged with a corresponding thread in the hub of the pinion 34. A lower portion of shaft 35 is of less diameter than the intermediate portion and affords at the intersection of such portions a shoulder 39. Such lower portion receives a washer 40, a spacer sleeve 41 and a gear 42 in the order named and these members are clamped together and against the shoulder 39 by a nut 43 threaded on shaft 3S. Beneath nut 43, the shaft has its lowermost portion rotatably mounted in a bearing in member 7. The spacer sleeve 41 is rotatably engaged in the member 19. Mounted on the intermediate portion of shaft 35 are an outer cup 44, resting on the washer and containing a suitable annular shock-absorbing cushion 45, an inner lcup 46 having a ange 47 resting on top of the cushion,'a spring 48 the lower end of which rests on the bottom of the inner cup, and a washer 49 resting on top of the spring. On the upper end of shaft 35 is a spacer sleeve 50; a spring 51 encompassing the sleeve; a washer 52 adjacent the upper end of the pinion 34 and screw 37, and slidably engaging sleeve 50; and a stop collar 53, recessed on its under side to receive the upper ends of the spring 51 and sleeve 50 and held to the latter by a snap ring 54, engaged in a circumferential groove in the upper end of shaft 35. When this shaft is rotated, the pinion 34 is prevented by its inertia from turning with the screw 38, whereby the latter advances the pinion upwardly, forcing the washer 52 upwardly and compressing spring 51 until the washer abuts the stop collar 53. The pinion 34 is then meshed with the flywheel gear 4 but it does not rotate until the screw is moved downwardly far enough to carry the washer 49 into abutment with the ange 47.'

Then the pinion 34 is compelled to rotate with the screw and turn gear 4 to crank the engine. When the engine starts, the flywheel gear 4, turning faster than shaft 35, causes the pinion 34 to move downwardly on screw 38 and become disengaged from flywheel 4 until it abuts washer 49, which is lifted by spring 48 back into the illustrated position.

The engine-starter drive is driven from armature shaft 15 through the intermediary of a clutch that responds toV the speed of this shaft, when driven by the engine faster i 'than a predetermined rate, to disconnect the starter drive.

This occurs as soon as the engine starts. The clutch includes a notched disk 56 (Fig. 3), mounted coaxially of shaft 15 to turn freely on hub 17, and a plurality (two as shown) of driving pawls 57, pivotally mounted on a 'carrier disk 58, which is xed to shaft 15. The notched disk has xed thereto a gear 59 which meshes with the gear 42 on the shaft 35 of engine-starter drive and drives the latter at the same speed but in the opposite direction. As shown, the notched disk 56 is held in axial position on hub 17 by and between a shoulder 60 on such hub and a snap ring 61, which is mounted in a circumferential groove in the hub. The pawl-carrying disk 58 is keyed to shaft 15 and clamped against a shoulder 62 on this shaft by means or a nut 63 which is threaded on the shaft and acts on the disk through the intermediary of the inner race of bearing 18. The disk 56 (Fig. 4) has a plurality (four as shown) of notches 64 formed in its outer periphery. This disk is intended to turn clockwise as viewed in Fig. 4. Each notch 64 has at its leading end a shoulderforming wall 65 ladapted to be engaged by the face 67 of the driving end 66 of pawl 57. The driving face 66 of each pawl is so related with the shoulder 65 which it engages that the pawl cannot be swung out of the notch by centrifugal force while the engine starter drive is under load. To release a pawl for outward swinging movement the disk 56 must be moved ahead of the driving end of the pawl far enough to enable the pawl to swing out of the notch. The disk 56, when not under load, can be moved ahead by cam action of the engaged face 67 and shoulder 65 when the pawl is moved outwardly by centrifugal force. The angular extent of the bottom wall of each notch should be suflicient to enable the pawl end 66 to be moved backwardly relatively to the notch far enough to carry its end lface 67 far enough away from wall 65 so that the pawl may move into and cut of the notch, when required.

The carrier disk 58 (Fig. 3) has fixed to its inner face at diametrically opposite points, two headed studs 68, which pivotally support, one on each, the pawls 57. Each pawl (Fig. 6) is held in axial position between the head of its stud and a snap ring 69, engaged in a circumferential groove in the outer end of its stud. Each pawl 57 (Fig. 4) has iixed thereto a crank 70, which is slotted (Fig. 6) to receive the rounded end of a bar 71, which is pivotally connected tol the crank by a pin 72. The latter has a head 73 which extends upwardly into a slot 74 in the carrier disk 58. The axis of curvature of this slot (Fig. 5) is the pivotal axis 68 of the pawl and the movement of the pawl is limited by the engagement of the head 73 with the ends of the slot. The rear end of the shank of bar 71 (Figs. 6 and 7) passes through an opening in an ear 75 struck out from the carrier disk 58. A spring 76 l encompasses the shank of the bar and acts between a washer 77 which abuts the head of the bar and the ear 75 to swing the pawl 57 on its pivot. This spring, as shown in Fig. 4, is holding pawl 57 in its inner position engaged in notch 67 and then acts on the pawl with greatest etectiveness. When, however, the pawl is swung out of notch 64 as shown in Fig. 8 the spring exerts only a small force on the pawl because the longitudinal center lines of crank 70 and bar 71 will then lie nearly in the straight line, which interconnects the axis 68 of the pawl 57 and the center of the opening in ear 75. When, however, the pawl is swung back into a notch 64 into its inner position, the center lines of the bar 71 and crank 70 swing outwardly away from the described line of centers into a position in which the spring acts on the crank much more effectively and exerts a greater force to hold the pawls in their inner positions.

One example of a one-way clutch suitable for interconnecting the pulley 32 and armature shaft 15, is shown in Figs. 3 and l0. The pulley 32 has an annular recess in its lower face, which receives the upstanding rim 79 of a cup. The bottom 80 of this cup has a central hole,

through which a portion of shaft 15 passes', and, rests against a shoulder 81 on this shaft. A nut 82, threaded on the upper end of shaft 15, has a cylindrical portion 83 which passes through a washer 84 and a spacer sleeve 85 and clamps the washer against the top of the sleeve and the bottom of the latter against the bottom 80 of the cup. The pulley 32 revolves on sleeve 85 and,V isheld against axial displacement between washer 84 andthe bottom 80 of the cup. Mounted within this cup'are upper and lower notched disks. 86 of identical construction and a thin intervening disk 87. These three disks are clamped together and to the pulley 32 by means of three rivets 88. The notches 89 in the superposed disks 86 receive, one in each, rolls 90 and these rolls have circumferential grooves 91 to receive a portion of the circumferential edge of the intermediate thin disk 87, whereby the rolls are held in proper vertical position with their upper and lower end faces out of contact with the pulley 32 and the vbottom 80 of the cup. The leading end wall 92 of each notch 89 is deeper than the trailing Wall 93 and the lower edges of these two walls are interconnected by a curved wall '94 which provides a surface for wedging the adjacent roll l90 against the rim 79 of the cup, when the notched disks 86 rotate in the direction ofthe arrow, whereby the cup and shaft 15 will be driven from the pulley 32. However, if the shaft 15 is driven in the direction of the arrow, the rim 79 of the cup will carry the rolls 90 into the deep ends of their notches whereby the pulley 32 will not be driven.

The electrical circuits of the motor-generator are `of the usual and well known type. They are shown conventionally in Fig. ll. A storage battery 95, starter switch 96, motor eld winding 10, are connected in a series with the armature, wires 97 connecting these elements 95, 96 and to one pair of the brushes 98 that ride on commutator 14, the other pair of brushes 99 being grounded. The generator field 11 is connected in shunt with the armature winding by means of a wire 100 which connects one terminal of the field winding 11 to the brushes 98, the other terminal of the field winding being grounded as are the brushes 99. The generator is connected to the battery through the intermediary of the usual voltage regulator with cutout, herein designated conventionally at 101. A wire 102 connects wire 100 to the regulator 101 and a wire 103 connects the latter to the battery 95. On closing the switch 96, the iield winding 10 and armature winding will be energized from the battery 95 and the dynamo-electric machine will operate as a motor to crank the engine through one of the transmissions described. When the engine starts and switch 96 is opened, the armature will be driven from the engine through the other transmission described and the dynamo-electric machine will then function as a generator and charge the battery 95 under the control of the voltage regulator and cutout 101 in the usual and well known way.

In operation, one starts the engine by closing switch 96 which energizes the series eld and the armature windings of the dynamo-electric machine, causing the latter to operate as a motor and rotating armature shaft 15. The latter cannot turn pulley 32 because of the clutch shown in Figs. 3 and 10. The carrier 58, however, is rotated and, since its pawls 57 then have their driving ends 66 engaged one in each of two notches 64 of the notched disk 56, this disk and the attached gear 59 will be driven in a clockwise direction, turning gear 42 at the same speed in a counterclockwise direction. The screw shaft 35 of the engine-starter drive will thus be rotated. On the initial rotation of this shaft, the pinion 34 will be held from rotation by its inertia. Therefore, rotation of the screw 37 will cause the pinion 34 to rise and move into mesh with the flywheel gear 4. This pinion will rise until it lifts washer 52 into abutment with the lower face of the stop collar 53. Then, the screw will be forced downwardly until washer 49 abuts flange 47. The pinion will y.then be rotated to turn the ywheel gear 4 in a clockwise menti direction and start the engine. In particularY case, the motor, when under its load of cranking the engine, operates at a speed of about i800 R. P. M. As soon as the engine starts, the switch 96 will be opened, deenergizing the motor, and the pinion 34 will be moved downwardly out of mesh with the ywheel gear 4 because the latter will then be turning faster than shaft 35. The engine in this particular example, has a maximum speed of about 5000 R. P. M., and the described belt and pulley connections between the engine crankshaft and armature shaft 15 step the speed up 50% to a maximum of 7500 R. P. M. The overrunning clutch, shown in Figs. 3 and l0, enables the engine to drive the shaft 15 in a clockwise direction. As soon as the engine starts, shaft 15 and thus carrier 58, disk 56 and its connections to the enginestarter drive will be moving fast enough to cause the pawls 57 to be thrown outwardly by centrifugal'force. The disk 56, being then relieved of its load because of the disengagement of pinion 34 from engine ywheel 4, it will readily be moved ahead by the cam action of the faces 67 of the pawls on the faces 65 of the notches 64 as the pawls are swung outwardly by centrifugal force. Only a small force is necessary for this purpose because a very low spring pressure is exerted on the pawls. As a practical matter, the pawls 57 are disengaged from disk 56 immediately following disengagement of pinion 34 from ywheel 4. After such disengagement, the disk 56 may turn enough to cause a slight upward jump of pinion 34 but the latter will not have time to move back into mesh with the ywheel 4 before the pawls 57 have become completely disengaged from disk 56.

The engine, as it continues to operate, will drive the dynamo-electric machine as a generator and charge the storage battery whenever the generator is turning at sufcient speed. The pawls 57 will not become reengaged with notches in disk 56 until just prior to stopping of the engine, namely at stalling speed. The disk is then moving so slowly that the pawls will engage in the notches without shock or undue noise. Since the disk, although stationary, is not under load, reengagement of the pawls in notches of the disk can be eiected without imposing any substantial strain on the parts. It will be clear that the pawls should not be engaged with the disk until the time stated-that is, just prior to stopping. Otherwise, rotation of the disk might be affected to a degree suicient to l raise the pinion 34 of the engine-starter drive into mesh with the engine ywheel gear 4. Thus, it is essential to use the least spring pressure on the pawls that is compatible with stability of engagement of the pawls and disk. The springs are not relied on to hold the pawls 57 and disk 56 in driving engagement. That is done by the eugagement of the faces 65 and 67, when the parts are under load whereby the pawls cannot swing out merely by centrifugal force but only after a small amount of relative rotation, which cannot occur until the load is removed from disk 56. Thus, each spring 76 is made just sufficient to hold its pawl against the disk 56 without uttering. Then, the spring is arranged to act on its pawl through a crank 70 so that this very light spring is made to exert less and less force on the pawl as the latter is swung outwardly. When each pawl is in its outer position, as shown in Fig. 8, the center lines of crank 70 and rod 71 closely approach the line, which interconnects the center of stud 68 and the center of the hole in lug 75, whereby the force acting on the pawl to move its driving end 66 inwardly is at minimum and so low as not to be capable of moving the pawl inwardly until the opposing centrifugal force approaches a very low value, such as is available only at stalling speeds.

The invention thus provides improved driving transmissions for interconnecting an electric motor-generator with an internal combustion engine in such a manner that the motor may crank the engine and the engine may drive the generator to charge a storage battery, the transmissions being alternately and automatically rendered eiective, whenever required, the one to crank the enginefrom the motor' ad'th'e :other to drive the generator from the enginen ..;E

What is claimed is; i

1. The combination with a dynamo-electric machine adapted to function as a motor for cranking an internal combustion engine having a shaft with a geafrnthereon, and as a generator forv charging a storage battery, said machine having an armature shaft, of a first transmission for connecting said armature and engine shaftsand including a one-way clutch'enabling the ant-.attire shaft to be Vdriven by the engine shaft and preventing the armature shaft from driving the engine shaft, an engine-starter driver including a shaft'having a screwthreaded portion and a pinion mounted on such portion for movement longitudinally of the last-named shaft into and out of mesh with'said engine gear, and asecond transmission between the last-named shaft 'and armature shaft and including a centrifugal clutch responsive to the speed of thearmatureshaft for interrupting the second transmission when the engine starts and said pinion moves out of mesli with' said gear.

2;'The combination, as claimed in claim l, in which the centrifugal clutch includes a disk in driving engagement with the engine-starter shaft and provided with a notch in its periphery having at its leading end a shoulderforming wall, a carrier in driving engagement with the armature shaft, a pawl mounted on the carrier for movement of its driving end into and out of said notch, said end when moved into the notch adapted to engage said wall and drive said disk, and means tending to move said pawl into the notch, said pawl being movable out of said notch by centrifugal force, when the engine starts and said pinion moves out of mesh with said gear.

3. The combination, as claimed in claim 2, in which the driving end of the pawl and said wall have interengaging cam faces preventing movement of such end out of the notch by centrifugal force when said disk is under load and effecting an advance of the disk when unloaded by means of the cam action of said faces when the pawl is moved outwardly by centrifugal force.

4. The combination, as claimed in claim 2, and variable-pressure spring means acting on the pawl in opposition to centrifugal force, said means exerting minimum and very low pressure on the pawl when its driving end is disengaged from a notch to prevent such end from moving into the notch until the speed of the engine shaft decreases to stallingY speed and exerting maximum and much greater pressure on the pawl when its drivingend moves into a notch to provide a stable engagement,

5. The combination, as claimed` in claim 2, in which the pawl is pivoted to the carrier and has a crank, and a spring acts between a fixed point on the carrier and the outer end of said crank, the center lines of the crank and spring approaching a straight line interconnecting said point and the pivot of the pawl when the pawl is disengaged from the notch and moving away from such line when the pawl moves toward and into said notch.

6. The combination with an electric motor-generator having an armature shaft and adapted for cranking an internal combustion engine having a shaft with a gear thereon, of a first transmission for connecting said annature and engine shafts and comprising a driven element on the armature shaft, an endless exible member for connecting the driven member to afdriving part on the engine shaft, and a one-Way clutch enabling the armature shaft to be driven by the engine shaft and preventing the armature shaft from driving the engine shaft, an engine-starter 'drive including a shaft having a screw-threaded portion and a pinion mounted on such portion for movement longitudinally of said shaft into and out of mesh with said engine gear, a second transmission between the lastnamed shaft and armature shaft including a centrifugal clutch responsive to the speed of the armature shaft for interrupting the second transmission when such speed exceeds a predetermined value, a support adapted to be 'fixed to the engine'and to which said motor-generator is pivotally connected for movement about the axis of said vengine-starter drive to enable adjustment of the tension of said endless exible member, and means for clamping the motor-generator to said support in various positions of adjustment about said axis.

No references cited. 

